Project Summary. Social stress consistently alters physiological markers related to mental disorders including hypothalamus-pituitary-adrenal (HPA) axis dysregulation as well as an increase in proinflammatory, and a decrease in anti-inflammatory cytokines. Similar changes can be observed in response to obesogenic diets and in obesity. Importantly, the co-occurrence of social stress and the consumption of obesogenic diets during development are potent risk factors for both mental and metabolic disorders. A key question in the study of these disorders and their interaction concerns the temporal sequences and molecular mechanisms of long- term biological programming. In particular, which molecular changes translate into functional consequences relevant to mental health and metabolism often remains elusive. Prior evidence suggests that biological embedding via epigenetic modifications may translate environmental exposure into unfavorable developmental health outcomes. What is unclear, however, is how epigenetic changes emerge during development and how they influence disease trajectories. Cross-sectional epigenetic studies in humans are unable to disentangle the causal effects of these complex environmental factors and epigenetic adaptations. We propose to leverage samples collected as part of a funded longitudinal, postnatal developmental study in a non-human primate (NHP) model of social stress and obesity to examine the chronology and dynamics of stress- and diet-induced genome-wide modification of DNA methylation (DNAm) from birth to adolescence. The dynamic epigenetic changes will be related to relevant functional outcomes including neuroendocrine, inflammatory and behavioral phenotypes. Our goal is to examine the formation and function of DNAm patterns in response to social stress and obesogenic diet exposure in NHPs and to investigate their additive and distinct effect on functional outcomes relevant for mental and metabolic health. Our central hypotheses are that developmental exposure to social stress and an obesogenic diet in rhesus monkeys affect peripheral DNAm profiles that are in turn predictive of physiological markers related to stress and metabolism. We will test our hypotheses with two specific aims: 1) Determine and compare longitudinal DNAm profiles of HPA axis genes in NHPs exposed to social stress, an obesogenic diet and matched controls. Are DNAm changes predictive of physiological markers of stress, inflammation and metabolic trajectories? 2) Determine and compare genome-wide DNAm profiles in NHPs exposed to social stress, an obesogenic diet and matched controls. What are the broader molecular pathways and networks that change in response to social stress and obesogenic diet intake? Our proposal's significance lays in the fact that these longitudinal, controlled studies on detrimental environmental factors during development are not feasible in humans. Our NHP model offers a direct translational approach with the unique possibility to generate predictive markers for mental and metabolic trajectories in humans.